1. Field of the Invention
The present invention relates to an instantaneous interruption detection apparatus for detecting instantaneous interruption of a signal transmitted from an in-cylinder pressure sensor mounted on an internal combustion engine, and an internal combustion engine control apparatus including the instantaneous interruption detection apparatus.
2. Description of Related Art
Generally, an internal combustion engine having cylinders and a crank is provided with in-cylinder pressure sensors to measure the pressures inside the cylinders. The in-cylinder pressure sensors are connected to an ECU (Electronic Control Unit). This ECU controls the internal combustion engine by determining fuel injection timings, for example, in accordance with the in-cylinder pressure signals indicative of the in-cylinder pressures received from the in-cylinder pressure sensors. However, there may occur a case where transmission of the in-cylinder pressure signal from the in-cylinder sensor to the ECU is instantaneously interrupted due to corrosion or wear of a terminal provided for connection between the in-cylinder pressure sensor and the ECU (referred to as “instantaneous interruption” hereinafter). If such instantaneous interruption occurs, since the ECU is inputted with an incorrect in-cylinder pressure signal, and accordingly, improperly controls the internal combustion engine as a result of which harmful substance in exhaust gas is increased, the vehicle drivability is lowered, and the engine noise is increased.
Hence, it is strongly desired to develop an instantaneous interruption detection apparatus capable of detecting the instantaneous interruption of the in-cylinder pressure sensor. Meanwhile, Japanese Patent Application Laid-Open No. 2001-56271 describes a method of detecting noise superimposed on the in-cylinder pressure signal. It is possible to use this method to detect the instantaneous interruption of the in-cylinder pressure sensor as explained as follows. The in-cylinder pressure gradually changes with the change of the crank angle (the rotation angle of a crank of an internal combustion engine). Accordingly, since the derivative signal of the in-cylinder pressure signal is kept below a predetermined threshold as long as the instantaneous interruption does not occur, while if the instantaneous interruption occurs, it exceeds the predetermined threshold. Hence, by determining whether or not the derivative signal of the in-cylinder pressure signal exceeds the predetermined threshold, it is possible to determine occurrence of the instantaneous interruption.
Incidentally, in some cases, a noise eliminating means such as a filter circuit is provided between the in-cylinder pressure sensor and the ECU to remove the noise component from the in-cylinder pressure signal. In these cases, the ECU is inputted with the in-cylinder pressure signal from which the noise component has been removed (referred to as “noise-removed in-cylinder pressure signal” hereinafter). The waveform of the noise-removed in-cylinder pressure signal is dull compared to that of the in-cylinder pressure signal from which the noise component is not removed. Accordingly, it may occur that the deviation signal of the noise-removed in-cylinder pressure signal does not exceed the threshold even if the instantaneous interruption has occurred, because its value is smaller than that of the in-cylinder pressure signal from which the noise component is not removed by the noise eliminating means. As explained above, when the noise eliminating means is provided, there is a possibility that the instantaneous interruption of the in-cylinder pressure sensor cannot be detected, while on the other hand, when the noise eliminating means is not provided, the noise component cannot be removed from the in-cylinder pressure signal.